<style>
  body, html {
    margin: 0;
  }
</style>
<script>
window.addEventListener('DOMContentLoaded', () => {
  const container = document.createElement('div');
  document.body.appendChild(container);
  const shadow = container.attachShadow({mode: 'open'});
  const iframe = document.createElement('iframe');
  iframe.src = './grid.html';
  iframe.style.cssText = 'width: 300px; height: 300px; margin: 0; padding: 0; border: 0;';
  shadow.appendChild(iframe);
});
</script>
